Correction of selsyn transmitter errors



1947- J. F. MANILDl 2,432,029

' CORRECTION OF SELSYN TRANSMITTER ERRORS Filed Oct. 5, 1945 3Sheets-Sheet 1 a j 5. 5 l

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Filed Oct. 5, 1945 3 Sheets-Sheet 2 Dec. 2, 1947. AN| D 2,432,029

CORRECTION OF SELSYH TRANSMITTER ERRORS Filed Oct. 5, 1945 3Sheets-Sheet 3 T it J if) M) J0 I 4 m 4 INVENTOR. Jaszaa/ Fjflan /Hi BYA TTORNEYS l ,siPatg nted r resistor;

T-jPAIENT OFFICE CORRECTION OF SEIiSYN TRANSMITTER ERRORS J0sephF.'-=Manildi, Pasadena; Calif., assignor, by

* mesne assignments; to :Howe& Fa'nt. Inc., South.

-Norwalk,aGonn.,: a corporation 'of Delaware .:SAppIication October52,1945; Serial No. 620.548

This "invention relates to the correction. of

i transmission errorsiinherent in Selsyntransmission'systems.

lselsyn 'Z transmission systems, whether of I the 'Ihaveiadiscoveredthatallsuch inherenterrors may;becorrected-'byx'suit'able modifications of' the., transmitter resstancelfroml-the linear formin -"w'h'ichit is ordinarily :used. Thefollowing de-- sxscriptiorrwillcsetnout,in preferred and illustrativeform, the details of theiatpplication of my inven- 1 tion to athreewirefsystem: and will then po nt out the .applica'bili'tywof .theinvention 'stO 0l5h8I systems. *For the'purpose of suchdescription Irefer 130 the accompanying drawings, in which Fig. Lisa circuit diagramshowing the essentials'of a-usual'three-wire .Selsyn system; .3 'Fig. v2is a'idiagramxshowing the varia'tion 'be- :tween "transmitter I angle:and receiver angle;

Fig. 3 is a diagramshowing the angular error of the receiveriplottcdagainst transmitter angle;

Fig. 4 is adiag-ranr showing the variation of the 1 resistancemodification factor with transmitter wangle;

Bis ardiagram showing the dei' elop edshape 0f a sectoriof ar'nodifiedresistance; g 7.

Fig. -6 'is a diagram showing the;develop"edshape giof a completeresistor; Fig; 'I isarfragmentary perspe'c ti eof the re- 'slstor'ofFlgfi;

i Fig. -8 is a dla gramishowing another "typefiof 5 Fig. 9- is adia'grar'ii:showing(another-resistor *modification; and v 'Fig. "10 is aview-inxperspective"of'afiriodified 'form'iofthe new resis'tor;---and V"Figs. '11 and. 12 "are. diagrams showing; circuits "thatinay beusedwith the resistor-of Fig. 10. I

.Fig. ishows the essential electrical c rcuiting ofa,typical"three-wireselsyn'system, consisting essentially (of acirculart'ransmitter resistance R, to

which a potential difference is applied bydiarnetgrically' opposedbrushes-D and E}, and which is connected by the three wire circuit I''CCT, tothe delta wi-ndingsfi'. T. 8. of the receiver.

. ":"rh-e receivermaybe considered to be of the usual type with itsdelta-connected coils rotatingin a on two-pole magnetic field; orl asindicated in Fig.

I 1'. may be considered as having a two-pole magnet 'M rotating in thefield of thecoils.

In such a system, where transmitter resistance R is linear with relationto the angle 0. of transmitter rotation, it can be shown that Z 120 tangI 3 +tan 6 where 0 denotes the angle of rotation of the transmitterbrush from any zero point (such as marked vi 0 in Fig. l) where. a brushmakes direct connection with a circuit lead; and where 0 denotes thecorresponding angle of rotation of the rotary element of the receiver,assuming that the receiver stands at .all times in an equilibriumposition with reference to the distribution of magnetic forces'which arecontrolled by the transmitter. As seen by inspection of Equation 1 theangle 0' becomes equal to 0 for values of 0 equal to 0; 30, and, so on,as might be expected from the fact thatone of the transmitter brushes Bis in direct contact with a lead and the other brush B is inmid-position between two leads for every 60 position,- and that the twobrushes have a symmetric relation to one of the leads, andto the othertwo leads considered as a pair, at every intermediate 30 point (e. g.such a brush positionas shown in Fig. 1.) Fig. 2 shows receiver angle 0'plotted against transmitter angle 0, and

for comparison shows 0 plotted ideally as equal to 0/ Comparison of thetwo curves shows the variation between 0' and 0 for the first 60 oftransmitter rotation from a zero position. From Equation 1 it may bededuced that where 5 denotesth di'fierence'between 0 and 0;

that is, denotes the angle by which receiver angle 0 "-va'rie iromftransmitter angle 0...; Inspection 10f Equation 2 shows that B is equalto zerom ll,

transmitter angles-of 0, 30, 60 etc.; that B varies 'symr netricall withrelation toany one of those angular positions; and that s is negative(receiver lags) for the first 30 of transmitter ro- "tation from a zeroposition, and is positive (receiver leads) through the next 30 oftransmitter rotation from that zero position. Fig. 3 shows [3 plottedagainst 0 for the first 60 of transmitter angle. Negative maximum of 16' occurs at 0:1318', and an equal positive maximum oc- The curverepeats itself for each 60 of transmitter rotation following that shownin Fig. 3.

As may be noted from Equationswi and 2, the

error ,8 in-the standard Sels-yn system is inde pendent of theresistance values used in the transmitter, or the relation oii'liosevalues to the ,resistancevalucs; in the receit'erinthc paper which Ilater refer to. I show among other things that, to obtain maximum torquein the receiver in where R1 is the resistance of the transmitterresistance per degree, R: the similar unit resistance of the receiverwinding, E the applied E, M. F., and P the maximumpower consumed in thesystem. However, those considerations of maximum torque do not affectthe receiver error, nor do they eifect the correction provided by myinvention.

In my invention, the transmitter resistance is varied from its usuallinear form by a factor which is a function of the transmitter angle 0.As a result of that resistance variation receiver angle is made to beequal to transmitter angle 0 for all values of the latter. The requisitevariation of the transmitter resistance is arrived at as outlined below.

Since the receiver error, in a system having a linear transmitterresistance (Ri=constant) is symmetric with relation to each 30 positionof the transmitter, it is only necessary to ascertain the requireddeviation of transmitter resistance for transmitter angles from 0 tothen to make the deviations from 30 to 60 symmetrical with those from 30to 0, and then to repeat the cycle of deviation for each succeeding 60of transmitter angle.

Referring to Fig. 1, and assuming that the resistance of a lineartransmitter resistance element is R1 per degree, or 120 R1 for each legbetween leads C, we let (1R1 represent the ideal unit resistance of atransmitter. That is, a is a function of a, the transmitter angle, suchthat 0', receiver angle, will become equal to 0, transmitter angle.

From consideration of the circuit of Fig. 1, and equivalent electricalcircuits derivable therefrom, it can be shown that the receiver angle 0'will be given as follows. Equation 1 above may be written,

In that equation, receiver angle a will be given with a substituted for0; thus,

Solving for or under those conditions, we obtain,

. 22m (h) 05 tan 0 which gives the necessary variation of a with 0 forzero error, and hence the variation of transmitter resistance with 0,since the resistance of the transmitter resistor element is, bydefinition, ClRl. a is the variable modification factor for R1, for zeroerror, expressing the variation of the resistance with 0, thetransmitter angle. Here again it is noted that the modification factoris independent of R1 and R2. and hence is applicable to any transmitterand any receiver or set of paralleled receivers. Fig. 4 shows thevariation of a 4 with I. along with a linear variation for comparison. v

The usual physical form of transmitter resistance element is one inwhich a toroidal coil -is wound helically about a toroidal form whichhas the shape of a section of thin walled tube with the ends of thesection normal to the axis. Fig. 5 shows at OABC a development of thesuperficial area of such an element from 0 to 30, and shows at OABC' thecorresponding development of a resistance element in which one edge,C'B, is shaped for zero error. In any such resistance element. theresistance at any transmitter angle 0 is equal to the area under C'B'between 00' and the vertical corresponding to 0.

Using Equation 6 and the fact that the area under CB representsnon-varying resistance with respect to 0, and that the area under C'B'represents the same for a function of 0 which satisfies Equation 6, itcan be shown that,

as 1 3 (ficosH-sind) where L is equal to the height or length of anequivalent (equal total resistance) resistor-the dimension 00 in Fig. 5.Fig. 5 shows 1"(0) as the curve C'B' plotted against 8 from 0' to 30.The plot for 30 to 60 is symmetric with C'B'. about the 30 axis. Thedeveloped shape of the whole toroidal resistor then follows with fivesuccessive duplications of the shape of the first 60; such completedeveloped shape being indicated in F g. 6.

Fig. 7 is a fragmentary perspective illustrating the physical form ofthe resultant resistor. In Fig. 7 the thin tubular body is shown at 20,and the helically wound resistance wire is fragmentariiy shown at I. Ashere shown all of the resistance variation is applied to one edge of theresistor body; but it will readily be understood that the. variationswhich are represented by Equation '7 above may be as well distributedbetween the two edges.

The fully detailed derivations of the several formulae given here arecontained in a paper by this applicant, published in Trans. A. I. E. E.July 1945, vol. 64. A copy of that paper is filed here-- with forreference.

Other physical forms of resistor may be used. For instance, as indicatedin Fig. 8, the modifying factor represented by Equation 6 may be appliedto a varying thickness of a toroidal body 20a on which the coil wire Ilais wound. "And Fig. 9 shows a commutator type resistor with resistanceelements Rs between successive commutator segments 22. In such aresistor the resistance variation will follow Equation 6 step by step.

By considerations and developments which are v tan 0 i-i-tan 0 and thefollowing equation Equation 7 above.

recti'on factor) -as given by Equations 6 and 6a above the following.generalization may be made.

where (1 represents the numeric value in degrees of the angle betweensuccessive connections to the resistor, and where n represents a numericconstant. v

Similarly the following generalization can be made as between Equations7 and 7a where n equals the angle between successive con.

nections to the resistor, in degrees, divided by 180, and where nrepresents a numeric constant.

A form of the new resistor R having four equi-.

angularly spaced leads is illustrated in Fig. 10. This resistor includesa thin tubular core 30. upon which is helically wound the resistancewire 3|. One end edge of the core is formed with projections spaced 90to produce the desired variations and the connecting wires 32, II, M, 35tap the resistor at the points of the projections F, G, H, and J.

In Fig. 11, the system shown includes the resistor R. of Fig. 10 withthe connecting wires 32, I3, 34, leading, respectively, from points F,G, H, and J on the resistor to the ends F, G. H, and J or independentreceiver coils 36, 31, extending at right angles to one another. Thereceiver is shown as including a magnet M rotating in the field of thecoils.

In Fig. 12, the system shown includes the resistor R of Fig. 10 withconnecting wires 32, 33, I4, 36 leading. respectively. to the ends F",G", H", and J" of delta-connected coils 38, 39, 40, and ll 01' thereceiver, which includes the magnet M.

I claim:

l. A circular resistor for a transmitter of a Selsyn system in which theresistor is tapped by equi-angularly spaced leads and is engaged byrelatively rotating contact members, said resistor having a resistancewhich varies in substantial accordance with the expression 1.2211. n'+tan 8 resistance which varies in substantial accordance with theexpression 120 tan 0 /+tan a I where 0 represents the relative angle ofrotation with respect to a predetermined zero point.

3. A circular resistor for a transmitter of a where 0 represents therelative angle of Selsyn system in which the resistor is tapped by iourequi-angularly spaced leads and is engaged by two diametrically opposedand relatively rotating contact members. said resistorhaving a Jresistance which varies in substantial accordance with the expressionrotation from a predetermined zero point.

4. A- toroidally wound resistance coil for a Selsyn system havingatransmitter in which the resistance coil is tapped by equi-angularlyspaced leads and is engaged by relatively rotating contact members, saidresistor having a superficial area which, measured from a predeterminedzero point, varies insubstantial accordance with the expression I 1cNamara-0 where n is equal to the angle between successive leadconnections to the resistor, in degrees, divided by 180, where n"represents a numeric constant, where 0 represents rotational angle fromthe predetermined zero point, and L represents a numeric constant.

5. A toroidally wound resistance coil for a Selsyn system having atransmitter in which the resistance coil is tapped by threeequi-angularly spaced leads and is engaged by two diametrically opposedand relatively rotating contact members, said resistor having asuperficial area which, measured from the predetermined zero point,varies in substantial accordance with the expression a (43' cos 0+sin 0)where L represents a numeric constant, and 0 represents rotational anglefrom the predetermined zero point.

6. A toroidally wound resistance coil for a Selsyn system having atransmitter in which the resistance coil is tapped by fourequi-angularly spaced leads and is'engaged by two diametrically opposedand relatively rotating contact members, said resistor having asuperficial area which, measured from the predetermined zero point,varies in substantial accordance with the expression 2 (cos 6+sin 0)where L represents a numeric constant and where 0 represents rotationalangle from the predetermined zero point.

JOSEPH F. MANILDI.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Great Britain Jan. 7, 1943 Certificate of"Correction Patent No. 2,432,029. Decemb'er'r2, 194?. JOSEPH F..'MANILDIIt is hereby certified that error appears in theprinted-specificationioi vthe..-above numbered patentrequiringcorrection aslfollowsz Column 3,"line,.3,rforthattportion ofthe equation reading (8=30, read (0'==30,; and thatthe.saridzLettersiPiatent should be read with thus correction thereinthatthesame'may conform to the' record of the case in the Patent- Oflice.

Signed and sealed" this 24th; day oiFebruary A. D.i1948.

THOMAS F; MURPHY,

Auiatmnt aIPatenu.

